1. Field of the Invention
The present invention relates to a plasma treatment apparatus, a method for forming a film with the use of the plasma treatment apparatus, and a method for manufacturing a thin film transistor with the use of the plasma treatment apparatus.
2. Description of the Related Art
There is a parallel plate plasma treatment apparatus provided with an upper electrode having a projected portion and a recessed portion in order to deposit a uniform film over a substrate with the use of a gas having high degradation efficiency and a gas having low degradation efficiency as material gases. In the plasma treatment apparatus, a gas having high degradation efficiency (O2) is introduced into a treatment chamber from an introduction port of a region of an upper electrode, which is near a lower electrode (that is, a surface of the projected portion of the upper electrode); a gas having low degradation efficiency (SiF4) is introduced into a treatment chamber from an introduction port of a region of the upper electrode, which is distant from the lower electrode (that is, a surface of the recessed portion of the upper electrode); a high-frequency voltage of 13.56 MHz is applied to the lower electrode; and a high-frequency voltage of 27.12 MHz is applied to the upper electrode, whereby plasma is generated between the lower electrode and the upper electrode. At this time, plasma is generated not only between a surface of projected portion of the upper electrode and a surface of the lower electrode but also in the depression of the upper electrode, so that a high density plasma region over the surface of the projected portion of the upper electrode is narrow in a direction perpendicular to a substrate provided over the lower electrode and a high density plasma region in the depression of the upper electrode is wide in a direction perpendicular to the substrate. Since the gas having low degradation efficiency is introduced into the high density plasma region in the depression of the upper electrode from the introduction port provided on the bottom of the depression, the gas having low degradation efficiency is exposed to plasma for a longer time than the gas having high degradation efficiency, which facilitates dissociation. As a result, the speed of plasma treatment can be increased, and the gas having low degradation efficiency is sufficiently dissociated, so that a uniform film can be deposited over the substrate (see Patent Document 1).